Coagulation is a very important process in rapid filtration system for effective removal of turbidity and organic matters in the sequential sedimentation and filtration processes. The purpose of this research is to find both coagulant consumption factors and to determine coagulant dosing equation with characteristics of water. Many coagulation factors are proposed such as pH, alkalinity, TOC, temperature, velocity gradient, mixing time, among these factors we have studied on the alkalinity and natural organic matter (NOM) as humic acid in pH 7.0∼7.5 value using two different coagulants; poly sulfate organic-magnesium (PSO-M) and poly aluminium chloride silicate (PACS). The results for coagulants consumption rates with alkalinity and NOM concentration showed that the dosing equation of PSO-M and PACS is as 10^((0.722log(alk)+0.00497)), 10^((1.06log(alk)-1.0)) for alkalinity and 6.1 ㎎/1, 5.l㎎/l for NOM, respectively.